The exchange of packetized information in wireless communication systems (or mobile communication networks) has already grown dramatically and probably will also grow in the future due to the rapid adoption of data services in mobile communication networks. Compared to voice services, data services require significantly more traffic and, hence, a much lower cost per bit is needed. A considerable effort has therefore been put in the development of standards for the LTE RAN (Long Term Evolution Radio Access Network) and EPC (Evolved Packet Core), which address these evolving needs.
Seamless mobility in cellular networks or mobile communication networks, like, e.g., LTE networks, is enabled by continued (radio) coverage (of user equipments) and respective communication within the mobile communication network, such as signaling among base transceiver stations (e.g. eNodeBs in LTE) and/or the hierarchically higher network nodes, such as, e.g., MMEs (Mobility Management Entities) and SGWs (Serving GateWays in LTE).
Most signaling messages in the context of ensuring the mobility functionality towards user equipments need to be exchanged between the source and the target base-transceiver stations (or source and target base station entities)—in case of such entities in the context of an LTE mobile communication network these are called eNBs (eNodeBs, or enhanced NodeBs).
In order to allow mobility-related signaling to be processed as much as possible locally (i.e. between base station entities) and to prevent hierarchically higher network nodes like MMEs and SGWs from bearing mobility-related signaling related to the whole customer base of the network operator, the concept of direct interfaces, like the X2 communication interface, has been introduced in LTE, i.e. a direct communication interface between a first and second base station entity to directly transmit information such as configuration information from the first base station entity to the second base station entity. The X2 communication interface is a type of communication interface between base station entities of a mobile communication network, especially a mobile communication network according to or using the Long Term Evolution (LTE) radio access technology. Typically, the X2 communication interface connects neighboring base station entities, typically enhanced NodeBs (or eNodeBs) in a peer to peer fashion to assist handover and provide for rapid co-ordination of radio resources.
In case of a handover event between two given base station entities that do not have an established X2 communication interface between them, the relevant handover-related information exchange can be transmitted using an S1 communication interface—which is a communication interface between, on the one hand, the eNodeBs (or base station entities) of the access network of the mobile communication network, and, on the other hand, specific network nodes of the mobile communication network, especially of the core network, such as MME nodes and/or SGW nodes—in order to perform the handover of the user equipment between the two involved base station entities, despite the fact that using the S1 communication interface for handovers causes a higher signaling load towards hierarchically higher (compared to the base station entities of the access network) network nodes like MMEs and SGWs.
Beside switching or exchanging user plane data between base station entities—e.g. the user plane data path from the source to the target base-transceiver station, especially in case of an actual or potential handover event of a user equipment between the base station entities—the X2 communication interface allows the exchange of mobility related signaling without the need to involve hierarchical higher network nodes, like MMEs and SGWs.
Via the X2 communication interface, all user equipment-associated signaling in the context of providing mobility-related services is bypassing the hierarchical higher network nodes (typically of the core network of the mobile communication network), like MMEs and SGWs. Thus, in case of frequent hand over events between two given base station entities, i.e. frequent mobility load between two eNodeBs, it is beneficial to set up an X2 communication interface between such base station entities, thus especially adjacent eNodeBs or base station entities having an overlapping or at least partly overlapping radio coverage area.
In order to provide a smooth mobility functionality, other configurations data—that are not triggered by a handover event, such as updating a changed physical cell identifier information or the like—can be exchanged, directly between two base station entities, using the X2 communication interface, i.e. via the X2 communication interface, such that configurations data or update information can be propagated within the access network of the mobile communication network in an autonomous manner through the involved base station entities and without the involvement of hierarchically higher network nodes (for triggering the propagation of such configuration information through the access network).
However, the number of X2 communication interfaces (or instances of the X2 communication interface) at a given base station entity is typically comparatively low when compared to the number of potentially neighboring base station entities having an at least partly overlapping radio coverage area—this being true especially in case that, as it is expected, a growing number base station entities providing or serving relatively small radio coverage areas (small radio cells) will be installed, especially in telecommunications networks having a layered structure (i.e. having (in a first layer) a number of radio cells aiming at providing radio coverage for a complete given geographical area, and additionally having (in a second layer) further radio cells at specific locations providing additional radio capacity and/or coverage on top of the radio coverage provided from the first layer for these specific locations).
As a result, there are and there will be a growing number of situations of neighboring base station entities that cannot be linked with each other by an X2 communication interface, and, hence, in order for configurations data or update information to be reliably propagated among a plurality of (neighboring) base station entities of the access network, there would be a direct involvement of hierarchically higher network nodes, i.e. each base station entity would individually receive an update information, e.g. via the S1 communication interface, that would be generated by the respective hierarchically higher specific network node.